1. The Field of the Invention
The present invention relates to systems, methods, and apparatus for coating medical devices with beneficial agents, such as medicinal agents including immuno-neutral chemicals.
2. Background and Relevant Art
In the medical fields, there are a number of devices that may be used inside a patient, whether on a temporary or permanent basis. For example, a medical practitioner may use various instruments or implants for various internal operating procedures, as well as instruments used to introduce other instruments or implants inside a patient. One common medical implant used in internal operations is a stent, which may be placed inside a patient's blood vessel.
In general, the various devices or objects that are inserted or implanted within a patient's body, whether on a temporary or permanent basis, often need to be coated with one or more beneficial agents. For example, the practitioner may desire for an implant to be coated with one or more chemicals configured to release a beneficial agent over time. In other cases, the practitioner may desire the implant to be coated with one or more immuno-neutral chemicals to ensure that the body does not reject the implant or instrument for some determined period.
There are a number of different devices or assemblies that can be used to coat a medical device or apparatus, such as a stent, with a beneficial agent (or, simply “agent.”) Some apparatus and techniques, such as those described in U.S. Pat. No. 5,464,650, involve applying an agent to a medical device using one or more agent coating rigs and corresponding sprayers (micromist devices). The spray apparatus used are generally configured to provide a “micromist.” Creating the micromist generally involves receiving the beneficial agent (such as dissolved within a polymeric compound) and applying air and/or ultrasonic forces to the agent. The air and/or ultrasonic forces, in turn, atomize (create particles of) the agent into the mist.
In conventional operation, therefore, a technician might position the medical device of interest in a micromist spraying apparatus. The spray apparatus might then rotate the medical device while a micromist nozzle sprays the atomized agent in mist form. Rotating and spraying the medical device in this manner is generally thought to distribute the agent on the medical device fairly evenly.
Unfortunately, there remain a number of different problems with these types of spraying or misting apparatus when coating a medical device with a beneficial agent. For example, there is often some variability in agent distribution across the medical device, and thus corresponding variability in agent concentration from device to device. Other disadvantages include difficulties controlling and maintaining drug concentration, verifying drug distribution or drug loading on any given device, and varying drug distribution in a controlled and predetermined manner to effect a more desirable drug loading profile. These differences in variability can be complicated by the fact that many medical devices have a varied surface area along their length.
In general, the problems with variability in spray distribution can be due to a wide range of factors in the construction of the conventional spray apparatus, as well as in the actual spray. For example, conventional spray apparatus are typically configured to hold one specific type of micromist nozzle, which usually means that a holding portion (nozzle adaptor) of the spray apparatus is configured for a specific dimension, thereby limiting the opportunity to vary the spray characteristics through changing the micromist nozzle. If there is a different, preferred micromist nozzle with a better distribution, the technician may be required to replace the entire spray/coating rig. While a technician can sometimes position a different micromist nozzle (having a similar dimensions) into the micromist nozzle adaptor, conventional apparatus are not configured to accommodate the different micromist nozzle's delivery parameters. For example, while conventional spray apparatus are configured to move the medical device horizontally with respect to the micromist nozzle's nozzle, conventional spray apparatus usually provide no vertical variability, which could be useful to accommodate differences between micromist nozzles.
Positioning of micromist nozzles and micromist nozzle types, however, is only one aspect of conventional spray apparatus that can cause agent distribution variability. Other aspects that can negatively affect agent distribution deal with the time needed to apply the agent. For example, conventional spray apparatus are usually optimized for delivering agent at about 2 to 10 psi of pressure. At this spray pressure, it usually takes a number of repeat passes before a medical device is sufficiently covered with the agent of interest.
The more passes that are needed to coat each medical device, however, the more likely there will be downtime to remove agent build up in the liquid feed nozzles and/or micromist nozzles. In particular, longer than necessary rates of use, or more frequent than necessary numbers of passes, per medical device can mean that a technician may need to clean the micromist nozzles more frequently than necessary. Despite the obvious disadvantages of associated downtime, buildup of agent in a liquid feed nozzle and/or micromist nozzle can also vary the evenness by which the technician is able to coat a medical device with beneficial agent.
Accordingly, there are a number of disadvantages with current micromist/spray rigs and apparatus in the art that can be addressed.